This invention is directed to a dual-rate coupling and bonded component therefor for transmitting drive torque to between drive and driven members. More particularly, the present invention is directed to a dual-rate coupling which has near zero stiffness at low torque loadings.
Drive couplings are known which transmit torque through an elastomer member, such as described in U.S. Pat. Nos. 4,772,245, 4,634,391, 4,516,956, 2,195,993, and 1,941,061. Single stage couplings have the problem in that at no-load or near no-load torques, a rattle may be produced between the drive and driven components that manifests itself as noise in the drive assembly. In addition to the obvious auditory irritation, the rattle produces accelerated wear on the chattering parts. To solve this, a low torsional stiffness is desired. However, the concomitant result of low torsional stiffness is large torsional windup. To solve this dilemma, dual-rate couplings have been developed which limit torsional deflections yet, at the same, time provide low initial stiffnesses. Such multi-rate couplings are described in U.S. Pat. Nos. 5,573,562, 5,522,747, 3,727,431, 3,438,222, 3,386,264, and 2,822,676. Notably, known dual-rate couplings may still provide an initial stiffness that is too great for some applications.
The dual-rate drive coupling of the present invention solves this rattle problem by providing very low, near zero stiffness at no-load or near no-load torques, yet provides a high stiffness for transmitting torques, when needed at higher torques.
Accordingly, the dual-rate drive coupling of the present invention comprises an inner member including a pair of snubbing arms; a pair of elastomeric arms extending outwardly from the inner member, each of the elastomeric arms having a length, a width and a thickness, where the length is greater than the thickness; and an outer member including a first pair of openings which receive the pair of elastomeric arms and a second pair of openings receiving the pair of snubbing arms, the pair of elastomeric arms interconnecting to said outer member at outer portions thereof whereby the pair of elastomeric arms exhibit near zero torsional stiffness and the pair of snubbing arms drivingly interconnect with the second pair of openings as torque increases above said minimum threshold torque level.
In another aspect, the pair of snubbing arms are coated on all surface portions engaging the second pair of openings with elastomer to prevent metal-to-metal contact. Preferably, the metallic portion of each of pair of snubbing arms tapers toward an outer end and a coating of elastomer is shaped to render the second pair of arms generally rectangular. In another aspect, the elastomer arms have at their terminus an enlarged portion which is received in similarly configured recesses formed in the outer member. Preferably, these enlarged portions are compressed within the similarly configured portions. To further prevent rotation, the enlarged protrusion preferably has an hyperextended portion which engages in a notch in a similarly configured portion of said outer member to provide an orientation feature. In another aspect of the invention, each of the pair of elastomer arms is compressed along their length in order to further reduce torsional stiffness. In yet another aspect, the elastomer arms have a slight curvature which skews the pair of radially extending snubbing arms within the second pair of openings, in a zero load condition, away from contact between a pair of drive surfaces on said pair of snubbing arms and said second pair of openings and a driven surface on said second pair of openings. This skewing of said pair of radially extending snubbing arms may be, at least in part, due to a characteristic premolded into said pair of elastomer arms.
Various other features, advantages and characteristics of the present invention will become apparent after a reading of the following detailed description of the preferred embodiments of the present invention.